Solving the Higgs Fine-Tuning Problem with Top Partners

Elin Bergeås Kuutmann
Elin Bergeås Kuutmann. Photo: Camilla Thulin.

The Knut and Alice Wallenberg Foundation granted in 2017 in total 560 million SEK in project grants for 2017 to 18 research projects which where assessed to hold the highest international standards and have the opportunity to lead to future scientific breakthroughs. The Department of Physics and Astronomy was fellow applicant in one of these projects that was granted 35.2 million SEK during five years.

Project Description

Project title: Solving the Higgs Fine-Tuning Problem with Top Partners
Main applicant: Sara Strandberg, Stockholm University
Fellow applicant: Elin Bergeås Kuutmann, division of High Energy Physics
Grant amount: 35.2 million SEK during five years
Funder: Project grant from the Knut and Alice Wallenberg Foundation

This project aims to find the underlying mechanism protecting the mass of the Higgs boson from large quantum corrections. The leading correction arises from the top quark, but can be cancelled by introducing top-quark partners to the theory. We will study possible signatures of such top partners and search for them using data from the ATLAS experiment at CERN’s Large Hadron Collider, which is expected to deliver a large data-set over the next six years.

Top partners are already being extensively searched for by the ATLAS experiment, with strong involvement by several of the team members. However, given the null results, it is becoming increasingly urgent to widen these searches to include the more complex signatures predicted by non-minimal models. As this task has both theoretical and experimental components, our team comprises a constellation of theorists with experience in model building and experimentalists with a longstanding experience in top-partner searches. The project will span over five years and will employ six PhD students and six postdoctoral fellows.

Our searches will cover the three most promising scenarios: direct searches for top partners in supersymmetry and compositeness models and indirect searches via precision measurements of processes involving top quarks. In each of these cases we will strive to pursue signals complementary to those usually targeted, with the intent of covering a large region of unexplored parameter space. Each search scenario will be coordinated by one or more senior team members.

At the end of the project we will either have found evidence for the existence of a top partner, or have put stringent limits falsifying a large group of extensions of the current theory. An additional benefit of the project will be the establishment of a long-term collaboration between experimental and theoretical particle physicists at different Swedish universities.

Sara Strandberg